<OSC Communication Function>
In a network including a plurality of nodes, communication between devices constituting each node is performed through an OSC line. OSC is an abbreviation of Optical Supervisory Channel. OSC is also called SV (supervisory) or Telemetry. Especially in a wavelength-multiplexed communication system, an OSC line is often realized using a wavelength different from that of a main signal. Each node has a function block (it is called such as a Circuit Pack, Package, Panel, unit, plug-in module) which sends and receives an OSC signal. This is called an “OSC package” in this specification for convenience. There is also a case where an OSC package unites with a management function block (system controller) of a node. Meanwhile, a “main signal” used in this document is a signal on which information that a transmission network has undertook its transmission from a client. On the other hand, an OSC signal is a signal for communication between devices within a transmission network.
An OSC package of each node is connected with its adjacent node via an OSC line, and they are always communicating with each other. Because a signal is received certainly by each node, a communication message between nodes away from each other is relayed and transmitted via OSC packages of intermediate nodes.
<The APR Function of ITU-T Recommendation G.664>
An optical transmission device and an optical transmission system are required to conform to the laser safety standard (IEC (International Electrotechnical Commission) 60825-2). In a wavelength-multiplexed optical communication system including optical amplification repeater nodes that is used widely today, it is required to prevent a laser beam of high power from being emitted from a portion that has been disconnected. For this reason, it is common that such wavelength-multiplexed optical communication system possesses an APR (Automatic Power Reduction) function recommended in ITU-T recommendation G.664, version 3 (March, 2006).
<A First APR Function Realization Method Related to the Present Application>
Function implementation of APR described in ITU-T (International Telecommunication Union Telecommunication Standardization Sector) recommendation G.664 will be explained using FIG. 5.
In FIG. 5 and in FIGS. 1, 3, 4 and 7 that will be described separately, description will be made in detail only about nodes on both sides of a section where a transmission line break occurs. Illustration of nodes besides those will be omitted or simplified. It is general that each optical amplifier includes in its input portion a monitor which detects existence or non-existence of an input signal. In FIG. 5 and FIGS. 1, 3, 4 and 7, only input signal monitors related to a described operation are illustrated, and illustration of monitors besides these are omitted. In a transmission line, it is general that a main signal occupying the majority of optical power and a signal of an optical monitoring line (hereinafter, referred to as “OSC (Optical Supervisory Channel) line”) are multiplexed to be transmitted. Also it is general that a multiplexer or a demultiplexer for this purpose is provided at an entrance and exit of a node to a transmission line. However, in FIG. 5 and FIGS. 1, 3, 4 and 7, illustration of these is omitted for simplification of description. In FIG. 5, the most general case in which a main signal and an OSC signal are transmitted in a same direction is described.
The first APR function realization method related to the present application is performed by a procedure of the following Steps S1 to S5. Meanwhile, Steps S1-S5 correspond to S1-S5 indicated in FIG. 5.
Step S1: A Cut occurs in a transmission line 31.
Step S2: A node 20 which is situated in the downstream side of a cut position detects that reception of both of a main signal from an optical amplifier 12WE and an OSC signal 33WE have stopped.
Step S3: The node 20 performs the following two operations toward a node 10 which is located in the upstream side of the cut position.
(1) To stop main signal output of an optical amplifier 22EW to a transmission line 32 which is the opposite transmission line of the cut line.
(2) To transmit an APR operating command for stopping main signal output of the optical amplifier 12WE performing output toward the cut position through an OSC line 34EW heading to the node 10.
Step S4: The node 10 detects that the main signal from the optical amplifier 22EW of the node 20 has stopped. Also, the node 10 receives the APR operating command through the OSC line 34EW.
Step S5: Upon detection of stopping of a main signal from the node 20 and reception of the APR operating command, the node 10 stops main signal output of the optical amplifier 12WE toward the cut position.
FIG. 6 is a diagram illustrating a situation after activation of APR by the first APR function realization method related to the present application. When the above described APR operation is activated by the node 10 and the node 20, influence shown in FIG. 6 occurs to nodes besides these.
In FIG. 6, first, output of a main signal toward the cutting occurrence section is stopped by APR control. The main signal to the cutting occurrence section is indicated by an outline arrow in FIG. 6. As it has been described with reference to FIG. 5, when an input main signal disappears (Loss of main signal), each optical amplifier stops output. Therefore, in the downstream side of the section where the signal disconnection has occurred, a shutdown by loss of an input main signal is chained. Thus, when an APR operation by the first APR realization method related to the present application is activated, transmission of a main signal is disrupted in both directions at the section in which APR has occurred.
Supplementary explanation of the operation of APR control mentioned above will be made.
As a cause of communication disruption of a main signal of the optical amplifier 12WE and the OSC signal 33WE, various causes such as a package failure and a wrong removal of internal wiring of a device besides cutting of a transmission line are also conceivable. For this reason, in Step S2, disruption of reception of both of a main signal and the OSC signal 33WE of the optical amplifier 12WE is made be a condition of activation of the APR operation.
When any of a main signal of the optical amplifier 12WE or the OSC signal 33WE is being transmitted, because it is certain that a transmission line is not cut, transmission in the upstream side does not need to be suspended. In other words, making stoppage of reception of both a main signal of the optical amplifier 12WE and the OSC signal 33WE be a condition of APR activation is an idea to avoid misjudgment that there is a transmission line break though a transmission line is normal. When it is not a transmission line break, it goes without saying that the maintenance workability is good if the APR operation is not performed.
There are two reasons for that, in Step S3, when activation of the APR operation is notified to the node 10 located in the upstream side of the cut position, main signal output of the optical amplifier 22EW is also stopped in addition to notifying it through the OSC line 34EW. Both of the reasons described below are caused by a matter that, although there is a possibility the transmission line 32 is also cut together with the transmission line 31, the node 20 cannot make confirmation about this.
One reason is that, because there is a possibility that the transmission line 32 is cut, it is necessary to stop output giving priority to safety even if it is not cut. The other reason is that, when the transmission line 32 has been also cut, although there is a possibility that the APR operating command for stopping main signal output of the optical amplifier 12WE has not been transmitted to the node 10 through the OSC line 34EW, there is no method to confirm that.
The reason that the APR operating command is notified through the OSC line 34EW is for prevention of false detection of an APR operation activation condition. In other words, in order for the node 10 to determine to activate an APR operation and stop main signal output to an APR activation section, the following two conditions have to be satisfied. The first condition is that a main signal from the node 20 is cut, and the second condition is that the OSC signal 34EW from the node 20 is cut or an APR operating command included in the OSC signal 34EW is received. By this duplication, true APR occurrence can be detected certainly while preventing the node 10 from wrongly detecting APR at the time of a failure, replacement and the like of the optical amplifier 22EW and an OSC package 21 of the node 20.
As shown in FIG. 6, in typical implementation of APR, a main signal in the transmission line 32 side that has a possibility not being cut is also cut. However, of course, there are some users who do not desire this. In other words, there is a desire to, when at least a line of one direction is alive, keep it alive.
<The Second APR Realization Method Related to the Present Application>
The second APR realization method related to the present application does not stop communication in the opposite side of a cut transmission line.
In the Appendix of ITU-T recommendation G.664, an APR operation which can stop a signal in the upstream side without making an impact on a main signal in the transmission line 32 side that has a possibility not being cut is described. FIG. 7 shows this method. When compared with FIG. 5, there is a feature that an OSC signal is transmitted to an opposite direction relative to a main signal. The APR operation will be described in turn.
Step S1: Cutting occurs to the transmission line 31.
Step S2: The node 10 that is located in the upstream side of the cut position detects that reception of an OSC signal 33EW from the node 20 situated in the downstream side of the cut position has stopped.
Step S3: By the stoppage of an OSC signal 33EW, the node 10 stops main signal output of the optical amplifier 12WE toward the cut position.
According to the second APR realization method related to the present invention, an APR operation can be performed for each one-way transmission line to which cutting has occurred. In other words, an APR operation can be performed without having an influence on a signal which passes the transmission line 32, the transmission line 32 being of an opposite direction of the transmission line 31 to which cutting has occurred and having a possibility not being cut.
Meanwhile, in U.S. Pat. No. 7,260,324, there is description about a signal transmitted in an opposite direction of a main signal in a 2-fiber Bi-directional optical transmission system (column 8, line 43 etc.). However, there is no detailed description about the signal in the specification.